Currently, belt-type continuously variable transmissions have been developed as driving transmissions for automobiles. A belt-type continuously variable transmission includes a V-belt wrapped around transmission pulleys provided on a drive shaft and a driven shaft with a variable gap interval therebetween. That is, the belt-type continuously variable transmission is capable of continuously changing the speed by changing the gap interval between the transmission pulleys.
As the V-belt wrapped around the belt-type continuously variable transmission, a high-load drive V-belt is known in the art, which includes at least one tension band extending in an endless loop, and a plurality of blocks engaged and secured thereto at a predetermined pitch in the belt length direction.
The high-load drive V-belt is provided with a plurality of outer receiving portions and inner receiving portions arranged in the belt length direction on the belt outer periphery surface side of the tension band and on the belt inner periphery surface side of the tension band, respectively. Each block is provided with an outer mating portion mating with the outer receiving portion and an inner mating portion mating with the inner receiving portion. With such a configuration, the plurality of blocks can be engaged and secured to the tension band.
The block includes a reinforcing member buried in a resin member. That is, the block includes the reinforcing member, and a contact portion having a contact surface to be in contact with a pulley and formed on each of the opposite side surfaces of the reinforcing member in the belt width direction. Note that the contact portion is formed by a resin.
The high-load drive V-belt transfers the driving force from a pulley to the tension band via the contact portion so that the power is transmitted by the tension band. Typically, the contact portion of the high-load drive V-belt is formed by a resin of a relatively high modulus of elasticity so as to efficiently transfer the driving force from the pulley to the tension band to thereby improve the power transmission property.
The thickness of the contact portion reduces through the wear of the contact surface during a run. Therefore, if the thickness of the contact portion in the direction perpendicular to the contact surface (hereinafter referred to simply as “the thickness of the contact portion”) is too small, the reinforcing member is exposed as the contact portion wears during a run so that the reinforcing member and the pulley may come into direct contact with each other. If the reinforcing member and the pulley come into direct contact with each other, the belt will be significantly damaged, thereby shortening the lifetime of the belt.
On the other hand, if the thickness of the contact portion is too large, there will be a relatively large shear stress at the interface between the reinforcing member and the contact portion during a belt run, and the contact portion may come off of the reinforcing member, thereby breaking the block. Therefore, in the prior art, in order to suppress the shear stress at the interface between the reinforcing member and the contact portion as much as possible while taking into consideration the wear from a belt run, the thickness of the contact portion is set to be as small as possible within a range that is greater than the wear from a belt run, e.g., 0.5 mm or more and 0.8 mm or less.
In the prior art, there is a demand for improving the wear resistance of the contact portion of such a high-load drive V-belt as described above. For this, Patent Document 1 is known in the art.
In Patent Document 1, the contact portion of a block of a high-load drive V-belt is formed by a phenol resin material containing a carbon fiber, wherein the carbon fiber is such that the thickness of the crystal layer is 25 angstroms or more and 200 angstroms or less in an onion structure. Thus, the flexural strength and the flexural modulus of elasticity of the contact portion are increased, thereby suppressing the wear of the contact portion.